Merge pull request #304 from luxonis/fov_tutorial

Added maximizing FoV docs

Author: Erol444

docs/source/_static/images/tutorials/fov.jpeg

@@ -78,6 +78,7 @@ Now, pick a tutorial or code sample and start utilizing Gen2 capabilities
    tutorials/hello_world.rst
    tutorials/multiple.rst
    tutorials/local_convert_openvino.rst
+   tutorials/maximize_fov.rst
 
 .. toctree::
    :maxdepth: 1

docs/source/index.rst

@@ -0,0 +1,32 @@
+How to maximize FOV
+===================
+
+By default, when you are using :code:`preview` output from :ref:`ColorCamera`, the DepthAI will crop the
+frames to get the desired aspect ratio. For example, if you are using Mobilenet-SSD model, you need
+:code:`300x300` frames. DepthAI will crop 1080P frames to :code:`1080x1080` and then resize them to :code:`300x300`.
+This means you will lose some part of the image.
+
+If you would like to maximize the FOV of the image, you can either:
+
+#. Change the aspect ratio (stretch the image)
+#. Apply letterboxing to the image
+
+Change aspect ratio
+*******************
+
+Use :code:`camRgb.setPreviewKeepAspectRatio(False)`. This means the aspect ratio will not be preserved and the image
+will be "stretched". This might be problematic for some off-the-shelf NN models, so model fine-tuning it might be required.
+`Usage example here <https://github.com/luxonis/depthai-python/blob/main/examples/rgb_mobilenet_4k.py#L42>`__.
+
+Letterboxing
+************
+
+`Letterboxing <https://en.wikipedia.org/wiki/Letterboxing_%28filming%29>`__ the frames. This method will decrease
+the size of the image and apply "black bars" above and below the image, so the aspect ratio is preserved. You can
+achieve this by using :ref:`ImageManip` with :code:`manip.setResizeThumbnail(x,y)` (for Mobilenet :code:`x=300,y=300`).
+The downside of using this method is that your actual image will be smaller, so some features might not be preserved,
+which can mean the NN accuracy could decrease.
+`Usage example here <https://github.com/luxonis/depthai-python/blob/main/examples/object_tracker_video.py#L44>`__.
+
+.. image:: /_static/images/tutorials/fov.jpeg
+